Collimator

ABSTRACT

A collimator having a front and rear and a longitudinal axis passing from the front to the rear. Spaced septa between the front and the rear defining openings and including a plurality of longitudinal sides parallel to the longitudinal axis and converging downwardly at different angles to form channels which converge to a single focal line. The septa further includes spaced parallel sides transverse to the longitudinal axis and intersecting with the longitudinal sides. The parallel sides form transverse channels which are non-focusing along the focal line.

United States Patent 1 Miraldi COLLIMATOR [75] Inventor: Floro D.Miraldi, Cleveland Heights,

Ohio

[73] Assignee: Case Western Reserve University, Cleveland, Ohio [22]Filed: June 25, 1971 [21] Appl. No.: 156,926

Related (1.8. Application Data [62] Division of Ser. No. 48,166, June22, 1970, Pat. No.

[ Dec. 4, 1973 OTHER PUBLICATIONS Tomographic Gamma-Ray Scanner byAnger, UCRL 16899 May 1966 pages 4-7 Longitudinal Tomographic by McAfeeet al., Journal of Nuclear Medicine, Vol. 10, No. 10 page 654, October1969.

Primary Examiner-Harold A. Dixon Attorney-Fay, Sharpe & Mulholland [57]ABSTRACT A collimator having a front and rear and a longitudinal axispassing from the front to the rear. Spaced septa between the front andthe rear defining openings and including a plurality of longitudinalsides parallel to the longitudinal axis and converging downwardly atdifferent angles to form channels which converge to a single focal line.The septa further includes spaced parallel sides transverse to thelongitudinal axis and intersecting with the longitudinal sides. Theparallel sides form transverse channels which are non-focusing along thefocal line.

2 Claims, 7 Drawing Figures PATENTED SHEEI 2 0F 3 PATENTED BEE 41975 sum3 or 3 PHOTQMULTIPLIER I I COLLIMATOR BACKGROUND OF THE INVENTION Inorder to study human or other organs the practice has developed ofmaking such organs radioactive. The patient usually takes medicationcontaining amounts of radioactive material.

The radioactive material which is commonly used gives off gamma rays. Itis usually easier and more effective to change the gamma rays to visiblelight radiation than to try to detect the gamma rays directly. However,the detection and conversion of gamma rays has its own difficulties.These problems include the discrimination between radiation resultingfrom photoelectric effect and compton effect and a determination of thelocation of the radiation within the source of radiation.

Many types of radiation scanners have been developed in order to detecta radiation pattern within the organs. In this respect, the followingarticles have been published:

l. Anger, H. 0.: The Scintillation Camera for Radioisotope Localization.[In] Radioisotope in der Localizationsdiagnostik, ed. by G. Hoffman andK. Scheer. Stuttgard, F. K. Schottauer, 1967.

2. Anger, H. 0.: Tomograhic Gamma-Ray Scanner with Simultaneous Readoutof Several Planes. UCRL-l6899 Rev., April 1967.

3. Brownell, G. I...: Theory of Radioisotope Scanning. Internat. J.Appl. Radiation & Isotopes 3: 181-192, August 1958 4. Cassen, B., Gass,H., and Crandell, P.: Improved- Resolution Fast-Section Scanner. (abst.)J. Nuclear Med. 9:307, June 1968.

5. Cassen, B.: Nonfocused COllimator Channel Systems in Cross-TimeCorrelation Three- Dimensional Scanning. (abst.) J. Nuclear Med.:391,June 1969.

6. Davis, T. P., and Martone, R. J.: The Hybrid Radioisotope Scanner. J.Nuclear Med. 7:114-127,

. February 1966.

7. Glass, H. 1.: A Depth-Focusing Collimator for the Investigation ofthe Brain Cortex. [In] Medical Radiosiotope Scanning: Proc.Symp. on M.Radioisotope Scanning, Athens, Apr. -24, 1964. Vienna, IAEA, 1965, Vol.I, pp. 243-252.

8. Hisada, K. -I., Hiraki, T., Ohba, S., and Matsudaira, M.:Simultaneous Performance of Isosensitive Scanning and Bilaminoscanning.Radiology 882129-134, January 1957.

9. Kuhl, D. E., and Edwards, R. 0.: Image Separation RadioisotopeScanning. Radiology 80:653-661, April 1963.

10. Kuhl, D. E., and Edwards, R. 0.: Rapid Brain Scanner withSelf-Contained Computer and CRT Display for Both Rectilinear andTransverse Section Viewing. (abst.) J. Nuclear Med. 9:332, June 1968.

11. McRae, J and Anger, H. 0.: Initial Clinical Results Obtained withthe Multiplane Tomograph ic Gamma-Ray Scanner. (abst.) U. Nuclear Med.10: 356-257, June 1969.

12. Miraldi, F., DiChiro, G., and Skoff, G.: Evaluation of CurrentMethods of Radioisotope Tomography and Design of a New Device: TheTomoscanner. (abst.) K. J. Nuclear Med. 10: 358-359,

1me1969. l3. Patton, J., Brill, A. B., Erickson, J., Cook, W. E., andJohnston, R. E.: A New Approach to Mapping Three-DimensionalRadionuclide Distributions.

(abst.) J. Nuclear Med. 102363, June 1969. 14. Rotenberg, A. D.: BodyScanning. PhD. Thesis,

,Univ. of Toronto, November 1962, pp. 73-76. Past radiation sensitivescanners have been able to obtain relatively good resolution but haveinherent limitations. They are normally designed to be focused at asingle point or very small area passing through the source.Investigation of a large source requires an excessive amount of time inorder to scan the entire area under observation. As a practical matter,patients may the and move during the scan thus jeopardizing theinvestigation.

Scintillation cameras which generally. observe an area rather than apoint have sought to solve the excessive time problem of the scanner.They have been relatively successful in this respect since they takemuch less time than a scanner to observe a given area. However, thescintillation camera such as that disclosed in the Anger US. Pat. No.3,011,057 also has its limitations. Because it must observe a relativelylarge twodimensional area at one time, the resolution is not as good asa scanner. This results because the phototubes in the Anger patentobserve a large scintillation crystal and it views some scattering oflight.

The present invention relates to a radiation scanning device and, moreparticularly, to a device which is well adapted for mapping radioisotopedistributions within a human body. A number of schemes have beendeveloped for utilizing gamma detecting scintillation crystals forscanning selected portions of the human body to determine radioisotopedistributions. Most schemes however produce a two-dimensionalrepresentation of the three-dimensional distribution. This results in adecreased resolution of a lesion because of superimposing and overlyingactivity. To enhance the resolution, the use of body-section scanning isproposed. The layer-bylayer analysis which can be attained bytomoscanning allows a significant enhancement of detail and contrast byelimination of the superimposing and obscuring activity. Although manyapproaches to section scanning have been suggested and tried, all may begrouped intothe general procedure of scanning with collimators inclinedto the plane of interest. This method was initiated by others and oftengoes by the name longitudinal section scanning. The general procedure isto obtain separate scans with a collimator at various angles to theplane of interest. The resulting separate scans are superimposed to givea reinforcement at a given plane.

This invention has combined the advantages of a camera and a scanner inorder to provide a threedimensional well defined image which can beformed in a relatively short amount of time. This invention provides forthe use of an elongated collimator and a scintillation crystal whichusually view the entire width of the source. A single longitudinal scanenables the collimator to view the entire area of the source. A secondscan from a different direction provides enough additional informationfor determining the depth of the source.

This invention also provides a means and technique for detecting thelocations of scintillations in a crystal with a high degree of accuracyin order to provide good resolution of the source of the radiation. Thisimproved resolution is obtained by means of a system utilizinglogarithms of the amplitudes of the pulses emanating fromphotomultiplier tubes.

SUMMARY OF THE INVENTION This invention is directed to a collimatorwhich focuses to a single focal line. It includes a body having a frontand rear and a longitudinal axis passing therebetween. Spaced septadefine openings and include a plurality of longitudinal sides parallelto the longitudinal axis which converge downwardly at different anglesto form channels. The septa further include spaced parallel sidestransverse to the longitudinal axis and intersecting with thelongitudinal sides which form transverse channels which are non-focusingalong the focal line.

FIG. 1 is a schematic representation of the use of the invention of thisapplication.

FIG. 2 is a block diagram of the elements of this radiation sensitivedevice.

FIG. 3 is a perspective view of the collimator used in this system.

FIG. 4 is a cross-sectional view of an alternate type of collimator.

FIG. 5 is a top sectional view of still another alternate type ofcollimator.

FIG. 6 is a perspective view of the scintillation crystal.

FIG. 7 is a schematic representative of the combined scintillationcrystal and collimator.

PREFERRED EMBODIMENT General System As illustrated in FIG. 1, thisinvention generally relates to a device for sensing radiation from asource which can be an organ of a human body. An individual will, aftertaking a radioactive substance in medication, have a concentration ofradiation in a given organ 11.

The radiation emanating from the source 11, usually gamma rays, issensed by a detector 12. In a given position, the detector 12 has arectangular field 14 of sensing. In actual practice, the plane 14 has agiven depth so there is actually a wedge-shaped channel viewing thesource at any given moment.

The detector 12 is able to move in either direction across the sourceand thus detect the radiation. The detector 12 has a definite viewingangle that can be varied in order to view the source from differentdirections. As explained in more detail hereinafter viewing theradioactive source from different directions allows an investigation ofdifferent reference planes within the source. This type of study isgenerally referred to as tomography.

A block diagram of the system for the tomographic scanner of thisinvention is illustrated in FIG. 2. A collimator 16 intercepts radiationnormally gamma rays from a source and allows transmission of part to ascintillation crystal 18 which is usually in close proximity thereto.The scintillation crystal converts to gamma rays to visible light. Meansfor converting the visible light to electrical pulses includesphotomultiplier tubes 20 and 22 which are located at each end of thescintillation crystal 18. The electrical pulses are subsequentlytransmitted respectively to the amplifiers 24 and 26. The collimator,scintillation crystal, means for converting the visible light toelectrical pulses and necessary physical and/or electrical connectionsmake up the essentials of means for detecting radiation from a source ofradiation.

The amplifiers 24 and 26 transmit their signals to a pulse heightselector and a position selector which combines for a read out on acathode ray tube. The amplifiers as will be explained in more detailbelow change the amplitudes of the electrical pulses from thephotomultiplier tubes to logarithms of the amplitudes beforetransmitting them to the pulse height selector. The amplifier whichconverts the amplitudes to logarithms of the amplitudes, pulse heightselector and the necessary electrical connections make up a means foroperating on the output of the amplitudes of the electrical pulses inorder to produce a substantially constant output for radiation of givenenergy levels regardless of the position of scintillations in thecrystals.

Means for determining the positions of scintillations in the crystalinclude a position selector 28 which is basically circuitry forsubtracting the logarithms transmitted by the amplifier 24 and 26. Theposition selector 28 further includes mechanisms for scanning the sourcewhile recording information concerning the radiation and relativepositions of the scanner and source.

A known circuit 34 triggers a cathode ray tube 32 when the pulse heightselector accepts a signal. Simultaneously the position selector givesinformation to the cathode ray tube 32 in order to properly place thepulse on coordinate axes.

COLLIMATOR The collimator 16, illustrated in FIG. 3 has a front 36, rear38 and sides 39 and 40 A longitudinal axis passes from the front to therear. Septa 42 are generally parallel to each other from the front 36and to the rear 38. In this respect the septa form a non-focusing systemin the longitudinal direction of the collimator 16. The septa 42 formopenings or channels 44 with longitudinal sides 46 which are parallel tothe longitudinal axis and which converge downwardly to a single focalline 48.

An alternate embodiment of the collimator is illustrated in FIG. 4 andhas pairs of openings 50, 51, 52 and 53 defined by sides which convergedownwardly to different focal lines 54, 56, 58 and 60 respectively. Thefocal lines 54, 56, 58 and 60 are formed along a plane perpendicular tothe plane of the collimator in order to allow the collimator to beaimed. A cross-section of the collimator is illustrated in FIG. 4, andfocal lines 54, 56, 58 and 60 of the collimator extend the length of thecollimator. Bu utilization of focal lines at different distances fromthe collimator different depths and areas of viewing can be madesimultaneously. With the use of the collimator of FIG. 4, however, itwould be necessary to use a pair of scintillation crystals for each pairof openings 50 which meets at a common focal line.

The dimensions of the collimator are selected to provide a desiredresolution distance at the focal line and to have a field of view whichis as uniform as possible. In practice, focal lengths of 6 to 20 cm havebeen found to be successful. This collimator is of a general designwhich is a cross between a focusing collimator and a straight through ornon-focusing collimator because it is focusing in one direction andnon-focusing in the per pendicular direction. In general collimators arecom-v posed of a heavy dense material such as lead.

An alternate embodiment of the multiplane collimator of FIG. 4 is shownin FIG. 5 where the shape is circular and a series of channels in a ringform the set that refers to one plane. In this collimator system gammaray detection consists of a thin circular crystal and an array ofphotomultipliers as illustrated by the Anger U.S. Pat. No. 3,011,037which is incorporated by reference herein. A modification to the Angersumming circuit is necessary, however, in order to obtain depthinformation with this collimator. The Anger method yields coordinatepositions X and y of a scintillation as noted in FIG. 5. If, forexample, it is desired to consider depth layer 56 of FIG. 4, then onlythe response for the set'of channels 51 is wanted. In order to obtainthis response, the output of the Anger system must be transmitted toelectrical circuits which add the information as X plus y If this sumhas a value between A and A then the scintillation must have occurredfrom the set of channels 51. In a similar manner any other level can bedetermined. The net result is that the use of the collimator of FIG. 5and known circuitry can convert a two-dimensional camera such as Angersto a tomographic camera.

SCINTILLATION CRYSTAL As illustrated in FIGS. 6 and 7, the scintillationcrystal 86 has agenerally rectangular cross-section which is uniformalong its length. A rectangular cross-section was chosen because offavorable attenuation. Other configurations where the cross-sectionalheight is different than the width would also be acceptable. The height88 is greater than the width 90. A range of heights of 1 inch to 2inches for sodium iodide has been successfully used in this invention.It is anticipated, however, that deviations from this height may alsoprove successful. The width of the scintillation crystal isapproximately one-half inch and some deviation may also be made fromthis dimension. A coating 92 of highly reflective material such asmagnesium oxide covers the scintillation crystal 86 in order to decreasethe attenuation of radiation within the crystal.

In use, the scintillation crystal 86 is mounted in proximity to thecollimator as illustrated in FIG. 7. The collimator 88 is focused toconverge at a focal line 92. Radiation received within the wedge-shapedchannel 94 is received by and transmitted through the collimator 88 tothe scintillation crystal 86 where a scintillation occurs which changesgamma radiation to visible light.

While the channel 94 is wedge-shaped, the wedge is really a complexconfiguration. Its sides converge in a nearly linear fashion but areslightly curved. After the focal line the sides diverge more rapidlythan they converged.

The shape of the scintillation crystals was chosen to give anattenuation factor which would produce an acceptable slope to giverealistic differences of the logarithms of the amplitudes so they couldbe detected as well as to give enough amplitudes to maintain anacceptable uncertainty. In order to accomplish these ends thescintillation crystal was chosen to have a rectangular shape with aheight of approximately I to 2 inches and a width of approximatelyone-half inch. This particular shape gave an attenuation constant whichwas satisfactory. In order to keep the amplitude of the pulses withinthe scintillation crystal at a relatively high level so they could bedetected with acceptable uncertainty the scintillation crystal wascovered with a high reflective coating such as magnesium oxide.

It should be understood that while the above described preferredembodiments give specific details, modifications will be available tothose knowledgeable in the art. For example, scintillation crystalscould possibly be replaced by more sophisticated, solid state itemswhich translate gamma radiation to visible light radiation. I claim: 1.A collimator comprising: a body having a front and rear and alongitudinal axis passing from the front to therear; spaced septabetween the front and the rear defining openings and including aplurality of longitudinal sides parallel to the longitudinal axis, saidlongitudinal sides converging downwardly at different angles to formchannels which converge to a single focal line which is parallel to thelongitudinal axis of the collimator and the septa further includingspaced parallel sides transverse to the longitudinal axis andintersecting with the longitudinal sides, the parallel sides formingtransverse channels which are non-focusing along the focal line. 2. Thecollimator of claim 1 wherein the longitudinal sides are symmetric abouteither side of a line passing from the front to the rear and aresubstantially perpendicular to the parallel sides.

1. A collimator comprising: a body having a front and rear and alongitudinal axis passing from the front to the rear; spaced septabetween the front and the rear defining openings and including aplurality of longitudinal sides parallel to the longitudinal axis, saidlongitudinal sides converging downwardly at different angles to formchannels which converge to a single focal line which is parallel to thelongitudinal axis of the collimator and the septa further includingspaced parallel sides transverse to the longitudinal axis andintersecting with the longitudinal sides, the parallel sides formingtransverse channels which are non-focusing along the focal line.
 2. Thecollimator of claim 1 wherein the longitudinal sides are symmetric abouteither side of a line passing from the front to the rear and aresubstantially perpendicular to the parallel sides.